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Basin Centered Gas Accumulations - Fact or Fiction?

Steven M. Goolsby and Edward Coalson
Coyote Oil and Gas Exploration, LLC., Centennial, CO

The concept of large, pervasively gas-saturated basin-centered hydrocarbon accumulations has been used as an exploration tool for several decades, particularly in many basins in the Rocky Mountain region. The recognition of regionally-extensive gas-charged areas dates back to a least the early 1950s, and the use of the basin-centered gas accumulation (BCGA) model gained wide acceptance in the 1970s and 1980s. This exploration model dictates that the deeper portions of certain basins contain gas-charged reservoir systems and produce essentially no mobile water. Under these conditions, many workers believed that any well drilled in a BCGA would encounter gas-saturated rock, and that commercial deliverability was a function of finding a “sweet-spot” within the accumulation that exhibited sufficient permeability for good deliverability. However, drilling experience has shown that mobile water does occur in areas thought to be BCGA areas. The recognition of this mobile water has recently led some workers to argue that the BCGA paradigm should now be rejected as an exploration model. In contrast to this argument, there is strong evidence that the BCGA model is still a viable exploration model. This viewpoint recognizes that regionally-extensive gas accumulations are more complicated than that envisioned using an over-simplified model. Despite these complications, the BCGA model can still be used as an exploration model with which to identify and exploit gas reservoirs in many hydrocarbon regions.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado